The Imaging X-ray Polarimetry Explorer (IXPE) will expand the information space for study of cosmic sources, by adding polarization to the properties (time, energy, and position) observed in x-ray astronomy. Selected in 2017 January as a NASA Astrophysics Small Explorer (SMEX) mission, IXPE will be launched into an equatorial orbit in 2021. The IXPE observatory includes three identical x-ray telescopes, each comprising a 4-m-focal-length (grazing-incidence) mirror module assembly (MMA) and a polarization-sensitive (imaging) detector unit (DU). The optical bench separating the MMAs from the DUs is a deployable boom with a tip/tilt/rotation stage for DU-to-MMA (gang) alignment, similar to the configuration used for the NuSTAR observatory. The IXPE mission will provide scientifically meaningful measurements of the x-ray polarization of a few dozen sources in the 2-8 keV band, over the first two years of the mission. For several bright, extended x-ray sources (pulsar wind nebulae, supernova remnants, and an active-galaxy jet), IXPE observations will produce polarization maps indicating the magnetic structure of the synchrotron emitting regions. For many bright pulsating x-ray sources (isolated pulsars, accreting x-ray pulsars, and magnetars), IXPE observations will produce phase-resolved profiles of the polarization degree and position angle.

IXPE scientific payload comprises of three telescopes, each composed of a mirror and a photoelectric polarimeter based on the Gas Pixel Detector design. The three focal plane detectors, together with the unit which interfaces them to the spacecraft, are named IXPE Instrument and they will be built and calibrated in Italy; in this proceeding, we will present how IXPE Instrument will be calibrated, both on-ground and in-flight. The Instrument Calibration Equipment is being finalized at INAF-IAPS in Rome (Italy) to produce both polarized and unpolarized radiation, with a precise knowledge of direction, position, energy and polarization state of the incident beam. In flight, a set of four calibration sources based on radioactive material and mounted on a filter and calibration wheel will allow for the periodic calibration of all of the three IXPE focal plane detectors independently. A highly polarized source and an unpolarized one will be used to monitor the response to polarization; the remaining two will be used to calibrate the gain through the entire lifetime of the mission.

The Gas Pixel Detector (GPD) is an X-ray polarimeter that exploits the photoelectric effect to measure the polarization and to obtain the image of astrophysical sources. This detector is on board the IXPE (Imaging X-ray Polarimetry Explorer) mission selected by NASA in the framework of the Explorer program scheduled for the launch in 2021. We report on tests carried out with a laboratory prototype of the GPD to verify the performance as a function of the temperature in a large temperature range between 15&deg;C and 40&deg;C.

We report on the first measure of the polarization of a laboratory source with a continuum energy spectrum, which simulates the effect of a real astrophysical source, carried out with a prototype of the Gas Pixel Detector (GPD). This detector is an X-ray polarimeter exploiting the photoelectric effect both to measure the polarization and to obtain the image of astrophysical sources. The gas pixel detector will be the focal plane detector on board the IXPE (Imaging X-ray Polarimetry Explorer) mission selected by NASA in the framework of the Explorer program for a launch in 2021.

The Imaging X-ray Polarimetry Explorer (IXPE) will be the next SMEX mission launched by NASA in 2021 in collaboration with the Italian Space Agency (ASI). IXPE will perform groundbreaking measurements of imaging polarization in X-rays for a number of different classes of sources with three identical telescopes, finally (re)opening a window in the high energy Universe after more than 40 years since the first pioneering results. The unprecedented sensitivity of IXPE to polarization poses peculiar requirements on the payload calibration, e.g. the use of polarized and completely unpolarized radiation, both on ground and in orbit, and can not rely on a systematic comparison with results obtained by previous observatories. In this paper, we will present the IXPE calibration plan, describing both calibrations which will be performed on the detectors at INAF-IAPS in Rome (Italy) and the calibration on the mirror and detector assemblies which will be carried out at Marshall Space Flight Center in Huntsville, Alabama. On orbit calibrations, performed with calibrations sources mounted on a filter wheel and placed in front of each detector when necessary, will be presented as well.

IXPE, the Imaging X-ray Polarimetry Explorer, has been selected as a NASA SMEX mission to be flown in 2021. It will perform polarimetry resolved in energy, in time and in angle as a break-through in High Energy Astrophysics. IXPE promises to ’re-open’, after 40 years, a window in X-ray astronomy adding two more observables to the usual ones. It will directly measure the geometrical parameters of many different classes of sources eventually breaking possible degeneracies. The probed angular scales (30”) are capable of producing the first X-ray polarization maps of extended objects with scientifically relevant sensitivity. This will permit mapping the magnetic fields in Pulsar Wind Nebulae and Super-Nova Remnants at the acceleration sites of 10-100 TeV electrons. Additionally, it will probe vacuum birefringence effects in systems with magnetic fields far larger than those reachable with experiments on Earth. The payload of IXPE consists of three identical telescopes with mirrors provided by MSFC/NASA. The focal plane is provided by ASI with IAPS/INAF responsible for the overall instrument that includes detector units that are provided by INFN. ASI also provides, in kind, the Malindi Ground Station. LASP is responsible for the Mission Operation Center while the Science Operation Center is at MSFC. The operations phase lasts at least two years. All the data including those related to polarization will be made available quickly to the general user. In this paper we present the mission, its payload and we discuss a few examples of astrophysical targets.

eXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. Primary goals are the determination of the equation of state of matter at supra-nuclear density, the measurement of QED effects in highly magnetized star, and the study of accretion in the strong-field regime of gravity. Primary targets include isolated and binary neutron stars, strong magnetic field systems like magnetars, and stellar-mass and supermassive black holes. The mission carries a unique and unprecedented suite of state-of-the-art scientific instruments enabling for the first time ever the simultaneous spectral-timing-polarimetry studies of cosmic sources in the energy range from 0.5-30 keV (and beyond). Key elements of the payload are: the Spectroscopic Focusing Array (SFA) - a set of 11 X-ray optics for a total effective area of ∼0.9 m<sup>2</sup> and 0.6 m<sup>2</sup> at 2 keV and 6 keV respectively, equipped with Silicon Drift Detectors offering &lt;180 eV spectral resolution; the Large Area Detector (LAD) - a deployable set of 640 Silicon Drift Detectors, for a total effective area of ∼3.4 m<sup>2</sup>, between 6 and 10 keV, and spectral resolution better than 250 eV; the Polarimetry Focusing Array (PFA) – a set of 2 X-ray telescope, for a total effective area of 250 cm<sup>2</sup> at 2 keV, equipped with imaging gas pixel photoelectric polarimeters; the Wide Field Monitor (WFM) - a set of 3 coded mask wide field units, equipped with position-sensitive Silicon Drift Detectors, each covering a 90 degrees x 90 degrees field of view. The eXTP international consortium includes major institutions of the Chinese Academy of Sciences and Universities in China, as well as major institutions in several European countries and the United States. The predecessor of eXTP, the XTP mission concept, has been selected and funded as one of the so-called background missions in the Strategic Priority Space Science Program of the Chinese Academy of Sciences since 2011. The strong European participation has significantly enhanced the scientific capabilities of eXTP. The planned launch date of the mission is earlier than 2025.

XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to X-ray Astronomy. At the time of
writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the
polarimetry window in high energy Astrophysics after more than 4 decades thanks to a detector that efficiently
exploits the photoelectric effect and to X-ray optics with large effective area. XIPE uniqueness is time-spectrally-spatially-
resolved X-ray polarimetry as a breakthrough in high energy astrophysics and fundamental physics.
Indeed the payload consists of three Gas Pixel Detectors at the focus of three X-ray optics with a total effective
area larger than one XMM mirror but with a low weight. The payload is compatible with the fairing of the Vega
launcher. XIPE is designed as an observatory for X-ray astronomers with 75 % of the time dedicated to a Guest
Observer competitive program and it is organized as a consortium across Europe with main contributions from
Italy, Germany, Spain, United Kingdom, Poland, Sweden.

COMpton Polarimeter with Avalanche Silicon readout (COMPASS) is a research and development project that aims to measure the polarization of X-ray photons through Compton Scattering. The measurement is obtained by using a set of small rods of fast scintillation materials with both low-Z (as active scatterer) and high-Z (as absorber), all read-out with Silicon Photomultipliers. By this method we can operate scattering and absorbing elements in coincidence, in order to reduce the background.<p> </p> In the laboratory we are characterising the SiPMs using different types of scintillators and we are optimising the performances in terms of energy resolution, energy threshold and photon tagging efficiency.<p> </p> We aim to study the design of two types of satellite-borne instruments: a focal plane polarimeter to be coupled with multilayer optics for hard X-rays and a large area and wide field of view polarimeter for transients and Gamma Ray Bursts.<p> </p> In this paper we describe the status of the COMPASS project, we report about the laboratory measurements and we describe our future perspectives.

The Large Observatory For x-ray Timing (LOFT) is a mission concept which was proposed to ESA as M3 and M4 candidate in the framework of the Cosmic Vision 2015-2025 program. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behaviour of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, &gt;8m<sup>2</sup> effective area, 2-30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the current technical and programmatic status of the mission.

X-ray polarimetry is a hot topic and, as a matter of fact, a number of missions dedicated to the measurement of the polarization in the ∼2-8 keV energy range with photoelectric devices are under advanced study by space agencies. The Gas Pixel Detector (GPD), developed and continuously improved in Italy by Pisa INFN in collaboration with INAF-IAPS, is the only instrument able to perform imaging polarimetry; moreover, it can measure photon energy and time of arrival. In this paper, we report on the performance of a GPD prototype assembled with flight-like materials and procedures. The remarkably uniform operation over a long period of time assures a straightforward operation in orbit and support the high readiness level claimed for this instrument.

The calibration system for XIPE is aimed at providing a way to check and correct possible variations of performance of the Gas Pixel Detector during the three years of operation in orbit (plus two years of possible extended operation), while facilitating the observation of the celestial sources. This will be performed by using a filter wheel with a large heritage having a set of positions for the calibration and the observation systems. In particular, it will allow for correcting possible gain variation, for measuring the modulation factor using a polarized source, for removing non interesting bright sources in the field of view and for observing very bright celestial sources. The on-board calibration system is composed of three filter wheels, one for each detector and it is expected to operate for a small number of times during the year. Moreover, since it operates once at a time, within the observation mode, it allows for simultaneous calibration and acquisition from celestial sources on different detectors. In this paper we present the scope and the requirements of the on-board calibration system, its design, and a description of its possible use in space.

The Imaging X-ray Polarimetry Explorer (IXPE) expands observation space by simultaneously adding polarization measurements to the array of source properties currently measured (energy, time, and location). IXPE will thus open new dimensions for understanding how X-ray emission is produced in astrophysical objects, especially systems under extreme physical conditions—such as neutron stars and black holes. Polarization singularly probes physical anisotropies—ordered magnetic fields, aspheric matter distributions, or general relativistic coupling to black-hole spin—that are not otherwise measurable. Hence, IXPE complements all other investigations in high-energy astrophysics by adding important and relatively unexplored information to the parameter space for studying cosmic X-ray sources and processes, as well as for using extreme astrophysical environments as laboratories for fundamental physics.

X-ray polarimetric measurements are based on the study of distributions of the directions of scattered photons or photoelectrons and the search of a sinusoidal modulation with a period of π. We present a new simple tool based on a scatter plot of the modulation curve in which the counts in each angular bin are reported after a shifting by 1/4 of the period. The sinusoidal pattern is thus transformed in a circular plot whose radius is equal to the amplitude of the modulation, while for a not polarized radiation the scatter plot is reduced to a random point distribution centred at the mean frequency value. The advantage of this tool is that one can easily evaluate the statistical significance of the polarimetric detection and can obtain useful information on the quality of the measurement.

Advanced Astronomy for Heliophysics Plus (ADAHELI+) is a project concept for a small solar and space weather mission with a budget compatible with an European Space Agency (ESA) S-class mission, including launch, and a fast development cycle. ADAHELI+ was submitted to the European Space Agency by a European-wide consortium of solar physics research institutes in response to the “Call for a small mission opportunity for a launch in 2017,” of March 9, 2012. The ADAHELI+ project builds on the heritage of the former ADAHELI mission, which had successfully completed its phase-A study under the Italian Space Agency 2007 Small Mission Programme, thus proving the soundness and feasibility of its innovative low-budget design. ADAHELI+ is a solar space mission with two main instruments: ISODY+: an imager, based on Fabry–Pérot interferometers, whose design is optimized to the acquisition of highest cadence, long-duration, multiline spectropolarimetric images in the visible/near-infrared region of the solar spectrum. XSPO: an x-ray polarimeter for solar flares in x-rays with energies in the 15 to 35 keV range. ADAHELI+ is capable of performing observations that cannot be addressed by other currently planned solar space missions, due to their limited telemetry, or by ground-based facilities, due to the problematic effect of the terrestrial atmosphere.

The LAMP (Lightweight Asymmetry and Magnetism Probe) X-ray telescope is a mission concept to measure the polarization of X-ray astronomical sources at 250 eV via imaging mirrors that reflect at incidence angles near the polarization angle, i.e., 45 deg. Hence, it will require the adoption of multilayer coatings with a few nanometers dspacing in order to enhance the reflectivity. The nickel electroforming technology has already been successfully used to fabricate the high angular resolution imaging mirrors of the X-ray telescopes SAX, XMM-Newton, and Swift/XRT. We are investigating this consolidated technology as a possible technique to manufacture focusing mirrors for LAMP. Although the very good reflectivity performances of this kind of mirrors were already demonstrated in grazing incidence, the reflectivity and the scattering properties have not been tested directly at the unusually large angle of 45 deg. Other possible substrates are represented by thin glass foils or silicon wafers. In this paper we present the results of the X-ray reflectivity campaign performed at the BEAR beamline of Elettra - Sincrotrone Trieste on multilayer coatings of various composition (Cr/C, Co/C), deposited with different sputtering parameters on nickel, silicon, and glass substrates, using polarized X-rays in the spectral range 240 - 290 eV.

The Lightweight Asymmetry and Magnetism Probe (LAMP) is a micro-satellite mission concept dedicated for astronomical X-ray polarimetry and is currently under early phase study. It consists of segmented paraboloidal multilayer mirrors with a collecting area of about 1300 cm2 to reflect and focus 250 eV X-rays, which will be detected by position sensitive detectors at the focal plane. The primary targets of LAMP include the thermal emission from the surface of pulsars and synchrotron emission produced by relativistic jets in blazars. With the expected sensitivity, it will allow us to detect polarization or place a tight upper limit for about 10 pulsars and 20 blazars. In addition to measuring magnetic structures in these objects, LAMP will also enable us to discover bare quark stars if they exist, whose thermal emission is expected to be zero polarized, while the thermal emission from neutron stars is believed to be highly polarized due to plasma polarization and the quantum electrodynamics (QED) effect. Here we present an overview of the mission concept, its science objectives and simulated observational results.

The Large Observatory For x-ray Timing (LOFT) was studied within ESA M3 Cosmic Vision framework and participated in the final downselection for a launch slot in 2022-2024. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument, LOFT will study the behaviour of matter under extreme conditions, such as the strong gravitational field in the innermost regions of accretion flows close to black holes and neutron stars, and the supranuclear densities in the interior of neutron stars. The science payload is based on a Large Area Detector (LAD, 10 m<sup>2 </sup> effective area, 2-30 keV, 240 eV spectral resolution, 1&deg; collimated field of view) and a Wide Field Monitor (WFM, 2-50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g. GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the status of the mission at the end of its Phase A study.

The Gas Pixel Detector (GPD) is an imaging X-ray polarimeter with a moderate spectral resolution and a very good position resolution.<sup>1, 2</sup> The GPD derives this information from the true 2-d charge image of the photoelectron track produced in gas and collected by an ASIC CMOS chip after its drift and its multiplication. In this paper we report on the experimental results of the study of the effect of a strong magnetic field in reducing the diffusion and increasing the sensitivity for a GPD filled with one bar of He-DME 20-80. We generated a magnetic field of about 1600 Gauss by means of commercial magnets made of an alloy of Neodymium-Iron-Boron configured as one ring and one cylinder. We compared the pixel size distributions and the modulation curves with and without magnets at two different drift fields, corresponding to different nominal diffusion properties, with both polarized and unpolarized sources. The results obtained show that a not sensitive improvement is present at this fields implying that a much larger magnetic field is necessary with this mixture, albeit a shift on the position angle of the modulation curve, derived from a polarized source, is observed.

LOFT (Large Observatory for X-ray Timing) is one of the five candidates that were considered by ESA as an M3 mission (with launch in 2022-2024) and has been studied during an extensive assessment phase. It is specifically designed to perform fast X-ray timing and probe the status of the matter near black holes and neutron stars. Its pointed instrument is the Large Area Detector (LAD), a 10 m<sup>2</sup>-class instrument operating in the 2-30keV range, which holds the capability to revolutionise studies of variability from X-ray sources on the millisecond time scales. <p> </p>The LAD instrument has now completed the assessment phase but was not down-selected for launch. However, during the assessment, most of the trade-offs have been closed leading to a robust and well documented design that will be reproposed in future ESA calls. In this talk, we will summarize the characteristics of the LAD design and give an overview of the expectations for the instrument capabilities.

We show that meaningful, highly sensitive x-ray polarimetry with imaging capability is possible with a small
mission tailored to the NASA Explorer program. Such a mission—derived from the Imaging X-ray Polarimetry
Explorer (IXPE) proposed to a previous NASA call—takes advantage of progress in light-weight x-ray optics
and in gas pixel detectors to achieve sensitive time-resolved, spectrometric, imaging polarimetry. We outline the
main characteristics and requirements of this mission and provide a realistic assessment of its scientific utility
for modeling point-like and extended x-ray sources and for studying physical processes (including questions of
fundamental physics).

We describe here the session of measurements that allowed the imaging capabilities of the Gas Pixel Detector
at the focus of an X-ray optics to be assessed. Firstly laboratory measurements and Monte Carlo simulations
were performed in order to study the intrinsic position resolution of the detector. Then a stand-alone test of the
JET-X FM-2 optics was performed at the PANTER X-ray test facility on November 2012, showing basically no
variation with respect to the results obtained in 1996. Finally a session of measurements performed at the same
facility allowed the imaging capability of the GPD at the focus of this JET-X optics to be calibrated.

At the core of the AGILE scientific instrument, designed to operate on a satellite, there is the Gamma Ray
Imaging Detector (GRID) consisting of a Silicon Tracker (ST), a Cesium Iodide Mini-Calorimeter and an
Anti-Coincidence system of plastic scintillator bars. The ST needs an on-ground calibration with a γ-ray beam to
validate the simulation used to calculate the energy response function and the effective area versus the energy and
the direction of the γ rays. A tagged γ-ray beam line was designed at the Beam Test Facility (BTF) of the INFN
Laboratori Nazionali of Frascati (LNF), based on an electron beam generating γ rays through bremsstrahlung in
a position-sensitive target. The γ-ray energy is deduced by the difference with the post-bremsstrahlung electron
energy<sup>1-.2</sup> The electron energy is measured by a spectrometer consisting of a dipole magnet and an array of
position sensitive silicon strip detectors, the Photon Tagging System (PTS). The use of the combined BTF-PTS
system as tagged photon beam requires understanding the efficiency of γ-ray tagging, the probability of fake
tagging, the energy resolution and the relation of the PTS hit position versus the γ-ray energy. This paper
describes this study comparing data taken during the AGILE calibration occurred in 2005 with simulation.

The LOFT mission concept is one of four candidates selected by ESA for the M3 launch opportunity as Medium Size missions of the Cosmic Vision programme. The launch window is currently planned for between 2022 and 2024. LOFT is designed to exploit the diagnostics of rapid X-ray flux and spectral variability that directly probe the motion of matter down to distances very close to black holes and neutron stars, as well as the physical state of ultradense matter. These primary science goals will be addressed by a payload composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD is a collimated (&lt;1 degree field of view) experiment operating in the energy range 2-50 keV, with a 10 m<sup>2</sup> peak effective area and an energy resolution of 260 eV at 6 keV. The WFM will operate in the same energy range as the LAD, enabling simultaneous monitoring of a few-steradian wide field of view, with an angular resolution of &lt;5 arcmin. The LAD and WFM experiments will allow us to investigate variability from submillisecond QPO’s to yearlong transient outbursts. In this paper we report the current status of the project.

The Gas Pixel Detector, developed and continuously improved by Pisa INFN in collaboration with INAF-IAPS, can visualize the tracks produced within a low Z gas by photoelectrons of few keV. By reconstructing the impact point and the original direction of the photoelectrons, the GPD can measure the linear polarization of X-rays, while preserving the information on the absorption point, the energy and the time of arrival of individual photons. The Gas Pixel Detector filled with He-DME mixture at 1 bar is sensitive in the 2-10 keV energy range and this configuration has been the basis of a number of mission proposals, such as POLARIX or XPOL on-board XEUS/IXO, or the X-ray Imaging Polarimetry Explorer (XIPE) submitted in response to ESA small mission call in 2012. We have recently improved the design by modifying the geometry of the absorption cell to minimize any systematic effect which could leave a residual polarization signal for non polarized source. We report on the testing of this new concept with preliminary results on the new design performance.

The Scientific objectives of the LOFT mission, e.g., the study of the Neutron Star equation of state and of the
Strong Gravity, require accurate energy, time and flux calibration for the 516k channels of the SDD detectors, as
well as the knowledge of the detector dead time and of the detector response with respect to the incident angle
of the photons. We report here the evaluations made to assess the calibration issues for the LAD instrument.
The strategies for both ground and on-board calibrations, including astrophysical observations, show that the
goals are achievable within the current technologies.

The Large Observatory For X-ray Timing (LOFT), selectyed by ESA as one of the four Cosmic Visiion M3 candidate missions to undergo an assessment phase, will revolutionize the study of compact objects in our galaxy and of the brightest supermassive black holes in active galactic nuclei. The Large Area Detector (LAD), carrying an unprecedented effective area of 10 m2, is complemented by a coded-mask Wide Field Monitor, in charge of monitoring a large fraction of the sky potentially accesesible to the LAD, to provide the history and context for the sources observed by LAD and to trigger its observations on their most interesting and extreme states. In this paper we present detailed simulations of the imaging capabilities of the Silicon Drift Detectors developed for the LOFT Wide Field Monitor detection plane. The simulations explore a large parameter space for both the detector design and the environmental conditions, allowing us to optimize the detector characteristcs and demonstrating the X-ray imaging performance of the large-area SDDs in the 2-50 keV energy band.

AGILE is a &gamma;/X-ray telescope which has been in orbit since 23 April 2007. The
&gamma;-ray detector, AGILE-GRID,
has observed Galactic and extragalactic sources, many of which were collected in the first AGILE Catalog.
We present the calibration of the AGILE-GRID using in-flight data and updated Monte Carlo simulations,
producing response matrices for the effective area, energy dispersion, and point spread dispersion as a function
of pointing direction in instrument coordinates and energy.
We performed Monte Carlo simulations in GEANT3 at different
&gamma;-ray photon energies and incident angles,
using Kalman filter-based photon reconstruction and on-board and on-ground filters. Long integrations of in-flight observations of the Vela, Crab and Geminga sources in broad and narrow energy bands were used to validate

The background of the Gas Pixel Detector is expected to be negligible for polarimetry of point sources due
to the intrinsic low atomic number and density of the He-DME mixtures and to its imaging properties. Also
the background for extended sources is expected to be negligible at least down to the smallest flux for sensitive
polarimetry in a reasonable observing time. However in the spatial distribution of the background in a laboratory
environment we observed an accumulation on the edges of the sensitive plane due to the presence of the nearby
cell walls. We recently developed gas pixel detectors with a new design of the gas cell having a larger distance of
the walls from the sensitive plane. In this paper we compare the spatial distribution of the measured background
for the two design and their residual systematics. Also the impact of the background in the case of SgrB2 a faint
extended source in the galactic center region is evaluated.

Pyrolytic Graphite Sheets (PGSs) are produced as convenient thermal interfaces because the highly oriented
structure allows for an excellent thermal conductivity. Here we report on the fact that this material can also
diffract X-rays. We succeeded in diffracting 5.9 keV and continuum photons on a 25 &mu;m thick PGS, verifying
that the lattice spacing is 3.35 &Aring; as expected. The low cost, lightness and the possibility to curve such thin
sheets allow to think at new applications in X-ray astronomy.

The possibility to perform polarimetry in the soft X-ray energy band (2-10 keV) with the Gas Pixel Detector, filled with low Z mixtures, has been widely explored so far. The possibility to extend the technique to higher energies, in combination with multilayer optics, has been also hypothesized in the past, on the basis of simulations. Here we present a recent development to perform imaging polarimetry between 6 and 35 keV, employing a new design for the GPD, filled with a Ar-DME gas mixture at high pressure. In order to improve the efficiency by increasing the absorption gap, while preserving a good parallel electric field, we developed a new configuration characterized by a wider gas cell and a wider GEM. The uniform electric field allows to maintain high polarimetric capabilities without any decrease of spectroscopic and imaging properties. We present the first measurements of this prototype showing that it is now possible to perform imaging and spectro-polarimetry of hard X-ray sources.

The Large Observatory for X-ray Timing (LOFT) is one of the four candidate ESA M3 missions considered for launch in
the 2022 timeframe. It is specifically designed to perform fast X-ray timing and probe the status of the matter near black
holes and neutron stars. The LOFT scientific payload is composed of a Large Area Detector (LAD) and a Wide Field
Monitor (WFM). The LAD is a 10 m<sup>2</sup>-class pointed instrument with 20 times the collecting area of the best past timing
missions (such as RXTE) over the 2-30 keV range, which holds the capability to revolutionize studies of X-ray
variability down to the millisecond time scales. Its ground-breaking characteristic is a low mass per unit surface,
enabling an effective area of ~10 m<sup>2</sup> (@10 keV) at a reasonable weight. The development of such large but light
experiment, with low mass and power per unit area, is now made possible by the recent advancements in the field of
large-area silicon detectors - able to time tag an X-ray photon with an accuracy &lt;10 &mu;s and an energy resolution of ~260
eV at 6 keV - and capillary-plate X-ray collimators. In this paper, we will summarize the characteristics of the LAD
instrument and give an overview of its capabilities.

In the context of the design of wide-field of view experiments for X-ray astronomy, we studied the response to X-rays in
the range between 2 and 60 keV of a large area Silicon Drift Chamber originally designed for particle tracking in high
energy physics. We demonstrated excellent imaging and spectroscopy performance of monolithic 53 cm<sup>2</sup> detectors, with
position resolution as good as 30 &mu;m and energy resolution in the range 300-570 eV FWHM obtainable at room
temperature (20 &deg;C). In this paper we show the results of test campaigns at the X-ray facility at INAF/IASF Rome, aimed
at characterizing the detector performance by scanning the detector area with highly collimated spots of monochromatic
X-rays. In these tests we used a detector prototype equipped with discrete read-out front-end electronics.

The use of large-area, fine-pitch Silicon detectors has demonstrated the feasibility of wide field imaging experiments
requesting very low resources in terms of weight, volume, power and costs. The flying SuperAGILE instrument
is the first such experiment, adopting large-area Silicon microstrip detectors coupled to one-dimensional
coded masks. With less than 10 kg, 12 watt and 0.04 m<sup>3</sup> it provides 6-arcmin angular resolution over &gt;1 sr field
of view. Due to odd operational conditions, SuperAGILE works in the unfavourable energy range 18-60 keV. In
this paper we show that the use of innovative large-area Silicon Drift Detectors allows to design experiments with
arcmin-imaging performance over steradian-wide fields of view, in the energy range 2-50 keV, with spectroscopic
resolution in the range of 300-570 eV (FWHM) at room temperature. We will show the concept, design and
readiness of such an experiment, supported by laboratory tests on large-area prototypes. We will quantify the
expected performance in potential applications on X-ray astronomy missions for the observation and long-term
monitoring of Galactic and extragalactic transient and persistent sources, as well as localization and fine study
of the prompt emission of Gamma-Ray Bursts in soft X-rays.

The SuperAGILE experiment is the hard X-ray monitor of the AGILE mission. It is a 2 x one-dimensional imager, with
6-arcmin angular resolution in the energy range 18 - 60 keV and a field of view in excess of 1 steradian. SuperAGILE is
successfully operating in orbit since Summer 2007, providing long-term monitoring of bright sources and prompt
detection and localization of gamma-ray bursts. Starting on October 2009 the AGILE mission lost its reaction wheel and
the satellite attitude is no longer stabilized. The current mode of operation of the AGILE satellite is a Spinning Mode,
around the Sun-pointing direction, with an angular velocity of about 0.8 degree/s (corresponding to 8 times the
SuperAGILE point spread function every second). In these new conditions, SuperAGILE continuously scans a much
larger fraction of the sky, with much smaller exposure to each region. In this paper we review some of the results of the
first 2.5 years of "standard" operation of SuperAGILE, and show how new implementations in the data analysis software
allows to continue the hard X-ray sky monitoring by SuperAGILE also in the new attitude conditions.

The New Hard X-Ray Imaging and Polarimetric Mission makes a synergic use of Hard X-Ray Imaging, Spectroscopy
and Polarimetry, as independent diagnostic of the same physical systems. It exploits the technology of
multi-layer optics that, with a focal length of 10 m, allow for spectroscopic and imaging, with a resolution from
15 to 20 arcseconds, on the band 0.2 - 80 keV. One of the four telescopes is devoted to polarimetry. Since the
band of a photoelectric polarimeter is not that wide, we foresee two of them, one tuned on the lower energy band
(2-10 keV) and another one tuned on higher energies (6 - 35 keV). The blurring due to the inclined penetration
of photons in the gas , thanks to the long focal length is practically negligible. In practice the polarimeters fully
exploit the resolution the telescope and NHXM can perform angular resolved simultaneous spectroscopy and
polarimetry on the band 2 - 35 keV. We are also studying the possibility to extend the band up to 80 keV by
means of a focal plane scattering polarimeter.

The X-ray sky in high time resolution holds the key to a number of observables related to fundamental physics,
inaccessible to other types of investigations, such as imaging, spectroscopy and polarimetry. Strong gravity effects, the
measurement of the mass of black holes and neutron stars, the equation of state of ultradense matter are among the
objectives of such observations. The prospects for future, non-focused X-ray timing experiments after the exciting age of
RXTE/PCA are very uncertain, mostly due to the technological limitations that need to be faced to realize experiments
with effective areas in the range of several square meters, meeting the scientific requirements. We are developing large-area
monolithic Silicon drift detectors offering high time and energy resolution at room temperature, with modest
resources and operation complexity (e.g., read-out) per unit area. Based on the properties of the detector and read-out
electronics we measured in laboratory, we built a concept for a realistic unprecedented large mission devoted to X-ray
timing in the energy range 2-30 keV. We show that effective areas in the range of 10-15 square meters are within reach,
by using a conventional spacecraft platform and launcher.

We devised and built a versatile facility for the calibration of the next generation X-ray polarimeters with
unpolarized and polarized radiation. The former is produced at 5.9 keV by means of a Fe<sup>55</sup> radioactive source
or by X-ray tubes, while the latter is obtained by Bragg diffraction at nearly 45 degrees. Crystals tuned with
the emission lines of X-ray tubes with molybdenum, rhodium, calcium and titanium anodes are employed for
the efficient production of highly polarized photons at 2.29, 2.69, 3.69 and 4.51 keV respectively. Moreover
the continuum emission is exploited for the production of polarized photons at 1.65 keV and 2.04 keV and at
energies corresponding to the higher orders of diffraction. The photons are collimated by means of interchangeable
capillary plates and diaphragms, allowing a trade-off between collimation and high fluxes. The direction of the
beam is accurately arranged by means of high precision motorized stages, controlled via computer so that long
and automatic measurements can be done. Selecting the direction of polarization and the incidence point we can
map the response of imaging devices to both polarized and unpolarized radiation. Changing the inclination of
the beam we can study the systematic effects due to the focusing of grazing incidence optics and the feasibility
of instruments with large field of view.

The Gas Pixel Detector (GPD) is a new generation device which, thanks to its 50 &mu;m pixels, is capable of imaging
the photoelectrons tracks produced by photoelectric absorption in a gas. Since the direction of emission of the
photoelectrons is strongly correlated with the direction of polarization of the absorbed photons, this device has
been proposed as a polarimeter for the study of astrophysical sources, with a sensitivity far higher than the
instruments flown to date. The GPD has been always regarded as a focal plane instrument and then it has been
proposed to be included on the next generation space-borne missions together with a grazing incidence optics.
Instead in this paper we explore the feasibility of a new kind of application of the GPD and of the photoelectric
polarimeters in general, i.e. an instrument with a large field of view. By means of an analytical treatment
and measurements, we verify if it is possible to preserve the sensitivity to the polarization for inclined beams,
opening the way for the measurement of X-ray polarization for transient astrophysical sources. While severe
systematic effects arise for inclination greater than about 20 degrees, methods and algorithms to control them
are discussed.

The SuperAGILE experiment was launched on April 2007 onboard the Italian gamma-ray mission AGILE. With a field
of view of approximately one steradian and an angular resolution of 6 arcmin, SuperAGILE is imaging the X-ray sky in
two one-dimensional projections in the 18-60 keV energy range. After a ~2-month Commissioning Phase, SuperAGILE
was set in its nominal configuration at the beginning of Science Verification Phase in July 2007 and it is observing the
X-ray sky since then. In this paper we describe the in-orbit operations, the commissioning, science verification and inflight
calibration phases, and provide a brief summary of the scientific observations carried out until June 2008.

SuperAGILE (SA) is the hard X-ray monitor of the AGILE small satellite mission, launched on 23<sup>rd</sup> April 2007.
The monitor is based on four one-dimensional coded-mask detectors. In spite of the compactness (45&times;45&times;15 cm<sup>3</sup>)
and lightness (5 kg), the experiment has high angular resolution (6 arcmin) and point source location accuracy (<2
arcmin, for bright sources) for every position in the Field Of View (FOV). To achieve these imaging performances,
considerable efforts were made for the alignment procedures during the assembly of the experiment itself, and
with the rest of the satellite. Mechanical alignment were measured during all the assembly phases and before the
launch campaign. Moreover, a specific campaign was performed in the laboratory with radioactive calibration
sources to calibrate the imaging response on ground. A on-orbit calibration campaign was performed using the
Crab Nebula. Due to the huge satellite wobbling (1 deg) and continuous slewing (1 deg/day), a refined attitude
correction strategy has been implemented on photon-by-photon data to maintain the high imaging performances.
In this paper we summarize all the activities we performed for calibrating and optimizing the imaging capabilities,
from the assembly of the experiment to the on-orbit calibrations and we show the results achieved.

The development of micropixel gas detectors, capable to image tracks produced in a gas by photoelectrons,
makes possible to perform polarimetry of X-ray celestial sources in the focus of grazing incidence X-ray telescopes.
HXMT is a mission by the Chinese Space Agency aimed to survey the Hard X-ray Sky with Phoswich detectors, by
exploitation of the direct demodulation technique. Since a fraction of the HXMT time will be spent on dedicated
pointing of particular sources, it could host, with moderate additional resources a pair of X-ray telescopes, each
with a photoelectric X-ray polarimeter (EXP<sup>2</sup>, Efficient X-ray Photoelectric Polarimeter) in the focal plane. We
present the design of the telescopes and the focal plane instrumentation and discuss the performance of this
instrument to detect the degree and angle of linear polarization of some representative sources. Notwithstanding
the limited resources, the proposed instrument can represent a breakthrough in X-ray Polarimetry.

The XEUS mission incorporates two satellites: the Mirror Spacecraft with 5 m<sup>2</sup> of collecting area at 1 keV and
2 m<sup>2</sup> at 7 keV, and an imaging resolution of 5" HEW and the Payload Spacecraft which carries the focal plane
instrumentation. XEUS was submitted to ESA Cosmic Vision and was selected for an advanced study as a
large mission. The baseline design includes XPOL, a polarimeter based on the photoelectric effect, that takes
advantage of the large effective area which permits the study of the faint sources and of the long focal length,
resulting in a very good spatial resolution, which allows the study of spatial features in extended sources. We
show how, with XEUS, Polarimetry becomes an efficient tool at disposition of the Astronomical community.

The Italian small satellite mission AGILE has been launched the 23rd of April 2007. SuperAGILE is the solidstate
hard X-ray imager of the mission. It is a coded-mask imager, with six arcmin angular resolution, a field of
view in excess of 1 steradian, and a gross energy resolution. Ground calibration campaigns have been performed
in the last year to optimize the detector response, for the energy calibration, to obtain the effective area at
various angles for various energy bands, to study location accuracy and angular resolution. In this paper we
report the preliminary results achieved.
The AGILE satellite has just finished the first and larger part of its commissioning phase. SuperAGILE successfully
passed the commissioning tests, and it is now in its final configuration. It is observing the X-ray sky
since the end of June as a part of the Science Verification Phase. The in-flight calibrations has been started and
will ended at the end of October. We show the first data obtained with the instrument in the first months of
observations.

We devised and built a light, compact and transportable X-ray polarized source based on the Bragg diffraction
at nearly 45 degrees. The source is composed by a crystal coupled to a small power X-ray tube. The angles of
incidence are selected by means of two orthogonal capillary plates which, due to the small diameter holes (10
&mu;m) allow good collimation with limited sizes. All the orders of diffraction defined by the crystal lattice spacing
are polarized up to the maximum order limited by the X-ray tube voltage. Selecting suitably the crystal and the
X-ray tube, either the line or the continuum emission can be diffracted, producing polarized photons at different
energies. A very high degree of polarization and reasonable fluxes can be reached with a suitable choice of the
capillary plates collimation.
We present the source and test its performances with the production of nearly completely polarized radiation
at 2.6, 5.2, 3.7 and 7.4 keV thanks to the employment of graphite and aluminum crystals, with copper and calcium
X-ray tubes respectively. Triggered by the very compact design of the source, we also present a feasibility study
for an on-board polarized source, coupled to a radioactive Fe<sup>55</sup> nuclide and a PVC thin film, for the calibration
of the next generation space-borne X-ray polarimeters at 2.6 and 5.9 keV.

Development of multi-layer optics makes feasible the use of X-ray telescope at energy up to 60-80 keV: in this paper we discuss the extension of photoelectric polarimeter based on Micro Pattern Gas Chamber to high energy X-rays. We calculated the sensitivity with Neon and Argon based mixtures at high pressure with thick absorption gap: placing the MPGC at focus of a next generation multi-layer optics, galatic and extragalactic X-ray polarimetry can be done up till 30 keV.

The Flight Model of the SuperAGILE experiment was calibrated on-ground using an X-ray generator and individual radioactive sources at IASF Rome on August 2005. Here we describe the set-up, the measurements and the preliminary results of the calibration session carried out with the X-ray generator. The calibration with omnidirectional radioactive sources are reported elsewhere. The beam was collimated using a two slits system in order to reach a rectangular spot at the detector approximately 1800 &#956;m × 100 &#956;m in size. The long dimension was aligned with the detector strip, so that the short dimension could fall within one single detector strip (121 &#956;m wide). The detector was then slowly moved continuously such that the beam effectively scanned along the coding direction. This measurement was done both at detection plane level (i.e., without collimator and mask) to characterize the detector response, and at experiment level (i.e., with collimator, mask and digital electronics), to study the imaging response. Aim of this calibration is the measurement of the imaging response at 0, 10 and 20 degrees off-axis, with a parallel beam, although spatially limited to a ~2 mm long section of the coded mask.

We report on a large active area (15x15mm2), high channel density (470 pixels/mm2), self-triggering CMOS analog chip that we have developed as pixelized charge collecting electrode of a Micropattern Gas Detector. This device, which represents a big step forward both in terms of size and performance, is the last version of three generations of custom ASICs of increasing complexity. The CMOS pixel array has the top metal layer patterned in a matrix of 105600 hexagonal pixels at 50&#956;m pitch. Each pixel is directly connected to the underneath full electronics chain which has been realized in the remaining five metal and single poly-silicon layers of a standard 0.18&#956;m CMOS VLSI technology. The chip has customizable self-triggering capability and includes a signal pre-processing function for the automatic localization of the event coordinates. In this way it is possible to reduce significantly the readout time and the data volume by limiting the signal output only to those pixels belonging to the region of interest. The very small pixel area and the use of a deep sub-micron CMOS technology has brought the noise down to 50 electrons ENC.
Results from in depth tests of this device when coupled to a fine pitch (50&#956;m on a triangular pattern) Gas Electron Multiplier are presented. The matching of readout and gas amplification pitch allows getting optimal results. The application of this detector for Astronomical X-Ray Polarimetry is discussed. The experimental detector response to polarized and unpolarized X-ray radiation when working with two gas mixtures and two different photon energies is shown. Results from a full MonteCarlo simulation for several galactic and extragalactic astronomical sources are also reported.

XEUS is a large area telescope aiming to rise X-ray Astronomy to the level of Optical Astronomy in terms of
collecting areas. It will be based on two satellites, locked on a formation flight, one with the optics, one with
the focal plane. The present design of the focal plane foresees, as an auxiliary instrument, the inclusion of a
Polarimeter based on a Micropattern Chamber. We show how such a device is capable to solve open problems
on many classes of High Energy Astrophysics objects and to use X-ray sources as a laboratory for a substantial
progress on Fundamental Physics.

SuperAGILE is the hard X-ray (15-45 keV) imager for the gamma-ray mission AGILE, currently scheduled for
launch in early 2007. It is based on 4 Si-microstrip detectors, with a total geometric area of 1444 cm<sup>2</sup> (max
effective area 230 cm<sup>2</sup>), equipped with 4 one-dimensional coded masks. The 4 detectors are perpendicularly
oriented, in order to provide pairs of orthogonal one-dimensional images of the X-ray sky. The field of view
of each 1-D detector is 107° x 68°, at zero response, with an overlap in the central 68° x 68° area. The angular
resolution on axis is 6 arcmin. We present here the current status of the hardware development and the scientific
perspective.

We discuss a new class of Micro Pattern Gas Detectors, the Gas Pixel Detector (GPD), in which a complete integration between the gas amplification structure and the read-out electronics has been reached. An Application-Specific Integrated Circuit (ASIC) built in deep sub-micron technology has been developed to realize a monolithic device that is, at the same time, the pixelized charge collecting electrode and the amplifying, shaping and charge measuring front-end electronics. The CMOS chip has the top metal layer patterned in a matrix of 80 &#956;m pitch hexagonal pixels, each of them directly connected to the underneath electronics chain which has been realized in the remaining five layers of the 0.35 &#956;m VLSI technology. Results from tests of a first prototype of such detector with 2k pixels and a full scale version with 22k pixels are presented. The application of this device for Astronomical X-Ray Polarimetry is discussed. The experimental detector response to polarized and unpolarized X-ray radiation is shown. Results from a full MonteCarlo simulation for two astronomical sources, the Crab Nebula and the Hercules X1, are also reported.

The AGILE Mission will explore the gamma-ray Universe with a very innovative instrument combining for the first time a gamma-ray imager (sensitive in the range 30 MeV - 50 GeV) and a hard X-ray imager (sensitive in the range 15-45 keV). An optimal angular resolution and a large field of view are obtained by the use of state-of-the-art Silicon detectors integrated in a very compact instrument. AGILE will be operational at the beginning of 2007 and it will provide crucial data for the study of Active Galactic Nuclei, Gamma-Ray Bursts, unidentified gamma-ray sources, Galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing.

We present a concept study for a novel All Sky Monitor experiment employing very limited resources. Our experience in designing, building and testing SuperAGILE - the hard X-ray imager for the AGILE mission - has demonstrated the possibility to develop a medium-sensitivity, wide field imager, with (at launch stage) ~5.5 kg weight, 12 Watts power and 0.04 cubic meters volume. With these few resources, it can provide crossed one-dimensional images of 1/10<sup>th</sup> of the sky, with on-axis 6 arcminutes angular resolution and ~10 mCrab 1-day sensitivity in the 15-45 keV energy range. In this paper we introduce to the ASPEX (All Sky Project for Extraterrestrial X-rays) project and show how a much more efficient All Sky Monitor can now be designed using the same approach and techniques, overcoming a number of severe limitations suffered by SuperAGILE due to the context of the AGILE mission, for which it was designed. The low resources and its efficiency in localizing X-ray transients and in long-term monitoring the steady X-ray sky, make ASPEX a suitable option for several new mission concepts (e.g., PHAROS, ESTREMO, ...).

The Flight model of SuperAGILE experiment was calibrated on-ground on August 2005 at IASF-Rome laboratories using standard radioactive X-rays sources. These omnidirectional sources were positioned at approximately 2 meters distance from the experiment. A method to correct for the beam divergence has been developed in order to use these measurements to derive information about the point spread function of the experiment for infinite distance sources. In this paper we describe the set-up of the measurements, the method to correct for the beam divergence and show preliminary results of the data analysis.

X-Ray Polarimetry can be now performed by using a Micro Pattern Gas Chamber in the focus of a telescope. It
requires large area optics for most important scientific targets. But since the technique is additive a dedicated
mission with a cluster of small telescopes can perform many important measurements and bridge the 40 year gap
between OSO-8 data and future big telescopes such as XEUS. POLARIX has been conceived as such a pathfinder.
It is a Small Satellite based on the optics of JET-X. Two telescopes are available in flight configuration and three
more can be easily produced starting from the available superpolished mandrels. We show the capabilities of such
a cluster of telescopes each equipped with a focal plane photoelectric polarimeter and discuss a few alternative
solutions.

The AGILE gamma-ray mission is in its Phase C-D. The Engineering model of the Payload has been built and tested, and the construction of the flight model has started. We present here the status of the SuperAGILE experiment, the 15-40 keV imaging monitor, based on Silicon microstrip technology and equipped with one dimensional coded masks. We show the design of the experiment and the results of testing campaigns carried out on the engineering model of the experiment.

In this paper we describe the instrumentation and the software tools we developed to test the SuperAGILE Front-End Electronics (SAFEE) and Interface Electronics (SAIE). The SAFEE is based on twelve XAA1.2 ASICs (produced by IDE-AS). The Test Equipment hardware is composed of commercial VME modules and laboratory developed boards. Commercial VME boards were used for data acquisition and SAFEE handling. Laboratory developed boards provide signal conditioning, pulse generation, trigger system and timing. The VME based architecture assured a stable system for a period of years and a very high acquisition rate. The choice of 'laboratory-developed' boards allowed an easy and cost effective continuous improvement of the system.
Two Linux running PC were used, one for the "System Control" and data acquisition, the other one for data reduction and archiving. The s/w for DAQ, data-reduction, and analysis also was laboratory-developed and based on well-known tools.

The XAA1.2 chip is a low noise, self-triggered, data-driven and sparse readout ASIC chip with 128 input channels designed as a front-end electronic circuit for silicon-microstrip detectors and manufactured by Ideas ASA (Norway). The XAA1.2 has been selected as the front-end electronic circuit of the SuperAGILE experiment on-board the AGILE satellite mission. This chip underwent to extensive laboratory tests to evaluate its scientific performances. Particularly we have measured the electronic noise and threshold voltage in both configurations stand alone and bonded to a silicon microstrip detector and we have tested the chip thermal stability and radiation damage. In this paper we describe the measurements and we discuss the results.

AGILE is an ASI gamma-ray astrophysics space Mission which will operate in the 30 MeV - 50 GeV range with imaging capabilities also in the 10 - 40 keV range. Primary scientific goals include the study of AGNs, gamma-ray bursts, Galactic sources, unidentified gamma-ray sources, diffuse Galactic and extragalactic gamma-ray emission, high-precision timing studies, and Quantum Gravity testing. The AGILE scientific instrument is based on an innovative design of three detecting systems: (1) a Silicon Tracker, (2) a Mini-Calorimeter, and (3) an ultralight coded mask system with Si-detectors (Super-AGILE). AGILE is designed to provide: (1) excellent imaging in the energy bands 30 MeV-50 GeV (5-10 arcmin for intense sources) and 10-40 keV (1-3 arcmin); (2) optimal timing capabilities, with independent readout systems and minimal deadtimes for the Silicon Tracker, Super-AGILE and Mini-Calorimeter; (3) large field of view for the gamma-ray imaging detector (~3 sr) and Super-AGILE (~1 sr). AGILE will be the only Mission entirely dedicated to source detection above 30 MeV during the period 2004-2006.

SuperAGILE is the X-ray instrument of the AGILE Mission. It is a set of silicon micro-strip detectors tiles coupled with a tungsten coded mask. The front end electronics of SuperAGILE is based on 48 ASIC XAA1.2 chips, each one collecting and conditioning the signals from 128 strips of the detector. Since this chip was not developed as a radiation resistant component for space applications and in order to predict and prevent the potential problems deriving from the space radiation environment, we irradiated two of such chips with ions of different chemical specie, ranging from 16O to 127I. At the 15 MV Tandem accelerator of the Laboratori Nazionali INFN di Legnaro we measured the occurrence of latch-up and Single Event Upset and the effects due to the absorbed total dose on the supply currents and on the bias currents which control the performances of the chip. In this paper we discuss how the results can be scaled to the AGILE environment and the impact of these data on the experiment design and on the observing strategy.

We report on the development of a new higly efficient polarimeter, based on the photoelectric effect in gas, for the 2-10 keV energy range, a particularly interesting band for x-ray astronomy. We derive the polarization information by reconstructing the direction of photoelectron emission with a pixel gas detector. Attention is focused on the algorithms used in data analysis in order to maximize the sensitivity of the instrument. Monte Carlo simulation is also discussed in details.

We report on a new instrument that brings high efficiency to x-ray polarimetry, which is the last unexplored field of x-ray astronomy. It derives the polarization information from the tracks of the photoelectrons imaged by a finely subdivided gas pixel detector. The device can also do simultaneously good imaging, moderate spectroscopy and fast, high rate timing down to 150 eV. Moreover, being truly 2D, it is non dispersive and does not require rotation. The great immprovement of sensitivity will allow direct exploration of the most dramatic objects of the x-ray sky; with integrations of the order of one day we could perform polarimetry of Active Galactic Nuclei at the percent level, a breakthrough in this fascinating window of high energy astrophysics.

A Micropattern detector in the focus of a grazing incidence telescope is nowadays the most powerful tool to perform a sensitive and reliable measurement of the linear polarization of celestial X-ray sources. The actual implementation of such a completely new device results from a trade-off of various factors and can provide a break-through increase of sensitivity with respect to traditional instrumental approaches. The sensitivity depends on the effective area of the optics and the modulation factor and efficiency of the detector. The latter strongly depends on the filling gas through various factors, including the absorption probability, the length of track versus the pixel size, the blurring introduced by the lateral diffusion during the drift. We discuss the impact of the choice of the filling gas on the sensitivity and on the operative band of the instrument, while the noble gases drive the efficiency, the organic quenching gases impact both in reducing the scattering and producing most straight tracks and on reducing diffusion. Some design solution are discussed both for a low energy oriented and high energy oriented polarimeters.

AGILE is an innovative, cost-effective gamma-ray mission approved by the Italian Space Agency for the Program of Small Scientific Missions. The AGILE gamma-ray instrument is designed to detect and image photons in the 30 MeV - 50 GeV energy band with good sensitivity and very large field of view (FOV). AGILE is planned to be operational during the year 2002 and will be open to the international community for the study of gamma-ray sources. A main aim of the AGILE Data Handling system is to provide an on-board processing and filtering of events reducing the background rate to an acceptable value within a factor of 1 - 10 of the gamma-ray photon rate. In order to maximize the instrument FOV and detection efficiency for large-angle incident gamma-rays (and minimize the effect of particle backscattering from the mini-calorimeter), the data acquisition logic uses the combination of top and lateral AC signals and a coarse on-line direction reconstruction in the Si-tracker. Appropriate data buffers are envisioned to maximize data acquisition for impulsive gamma-ray events in the tracker and mini-calorimeter, respectively.

SuperAGILE is the X-ray stage of AGILE gamma-ray mission. It is devoted to monitor X-ray (10 - 40 keV) sources with a sensitivity better than 10 mCrab in one observing day and to detect X-ray transients in a field of view of 1.8 sr, well matched to that of the gamma ray tracker, with few arc-minutes position resolution. SuperAGILE is designed to exploit one additional layer of four silicon micro-strip detectors, for 1444 cm<SUP>2</SUP> of total geometrical area, on top of the AGILE tracker and a system of four mutually orthogonal one- dimensional coded masks to encode the X-ray sky. Low noise electronics based on ASICs technology is the front-end read out. We present here the instrumental and astrophysical performances of SuperAGILE as derived by Monte Carlo simulation and experimental tests.

The chip XA1.3, low noise, self-triggered, data-driven and sparse readout multichannel front-end integrated circuit (ASICs), underwent to extensive calibration and tests, included temperature tests and power consumption tests. We describe the results of the tests and calibration and their impact, as front-end of the silicon micro-strip detectors, on the scientific performances of SuperAGILE experiment.

The stellar x-ray polarimeter (SXRP) will be more than an order of magnitude more sensitive than any previous x-ray polarimeter in the 2 - 15 keV energy band. The SXRP is a focal plane detector for a Danish-Russian SODART telescope, which will be launched on the Russian spectrum-x-gamma (SXG) mission. The SXRP exploits the polarization dependence of Bragg reflection from a graphite crystal, and of Thomson scattering from a target of metallic lithium. The SXRP flight model (FM) was calibrated at a facility at Lawrence Livermore National Laboratory (LLNL) equipped with polarized and unpolarized x-ray sources producing x-rays in the band pass for the graphite and lithium scatterers. By adjusting the orientation of the SXRP with respect to the incident x-ray beam, it was possible to simulate the converging beam from a SODART telescope and to measure the SXRP response to telescope pointing errors. In this paper, we describe the SXRP-FM calibration and present results for the graphite polarimeter.

We present the results of the measurement of transparency of five round beryllium windows for the LEIPC (low energy imaging proportional counter) of the stellar x-ray polarimeter (SXRP) experiment which will be flown on board the spectrum x-gamma Russian satellite. Each window was tested across its entire surface by using an x-ray fluorescence beam produced by a Cm<SUP>244</SUP> alpha source. We mapped the physical properties of the whole set in order either to verify the performance of the manufacturing method and to select the window having the highest counting rate and the most homogeneous transparency. This is crucial in order to both enhance the scientific capability of the experiment and to reduce the impact of possible systematic effects due to pointing instability which could occur during the observation of celestial sources.

We measured the average anisotropy of the primary charge cloud produced by photoelectron when an x-ray beam linearly polarized is absorbed on a Ne-DME gas mixture by using a micro-gap proportional counter. This average anisotropy is not present when an Fe55 unpolarized x-ray source is used. We discuss the results of our measurement in terms of performances of this detector as an x-ray polarimeter.

The performance of the engineering prototype Stellar X-Ray Polarimeter (SXRP) has been evaluated. One hundred percent polarized monochromatic x rays at 2.6 keV and 9.7 keV were used to measure the response of the instrument in the energy bands of the graphite and lithium polarizing elements, respectively. On-line analysis showed that the respective depths of modulation are 96% ad 70% as expected. Irradiating SXRP with broadband unpolarized x rays in the energy band 2 - 17 keV demonstrated that the level of spurious modulation inherent in the instrument is less than 3%. Up-to-date results are presented and compared to the predictions of Monte Carlo simulations.

The Stellar X-ray Polarimeter (SXRP) will be the third orbiting stellar x-ray polarimeter, and should provide an order of magnitude increase in polarization sensitivity over its predecessors. The SXRP exploits the polarization dependence of reflection from a graphite Bragg crystal and scattering from a lithium Thomson scattering target to measure the linear polarization of x- rays from astrophysical sources. In this paper, we review the status of the SXRP instrument.

The Stellar X-Ray Polarimeter employs the same Imaging Proportional Counters for both the Bragg and the scattering stage. We show the main characteristics of these detectors and their performances on the basis of tests on the Technical Constructive Model and on the Engineering Models.

A 'phoswich' created by NaI(Tl and CsI(Na) crystals that are optically coupled via irradiation with 200 MeV protons is here used to simulate the effect on a satellite of an orbit below the radiation belts that cross the South Atlantic anomaly. Preliminary analysis of these data adumbrates the noise following activation, as well as the capabilities of a digital pulse-shape discriminator.

The Stellar X-Ray Polarimeter (SXRP) uses the polarization sensitivity of a graphite Bragg crystal and a lithium Thomsom scattering target to measure the polarization of X-rays from astrophysical sources. The SXRP is a focal plane detector for the Soviet-Danish SODART telescopes which will be launched on the Soviet Spectrum-X-Gamma mission. The SXRP will be the third orbiting stellar X-ray polarimeter, and should provide an order of magnitude increase in polarization sensitivity over its predecessors.

A hollow cylindrical proportional counter is the best choice for an X-ray polarimeter
based on the Thomson scattering. Here we report on the results of Montecarlo simulations
performed to optimize the geometrical configuration of such a polarimeter, conceived as a
focal plane instrument of an X-ray telescope. We also present the design characteristics of a
prototype of a cylindrical proportional counter, presently under testing in our laboratories.

Measurements performance on cylindrical scatterers for focal plane X-ray polarimetry consisting of beryllium capsules filled with metallic lithium are reported. The method used is discussed and evaluated based on the measurements.

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